1. Field of the Invention
Embodiments of the present invention generally relate to an apparatus and method for processing large area substrates. More particularly, embodiments of the present invention relate to a substrate support for supporting large area substrates in semiconductor processing and a method of fabricating the same.
2. Description of the Related Art
Equipment for processing large area substrates has become a substantial investment in manufacturing of flat panel displays including liquid crystal displays (LCDs) and plasma display panels (PDPs), organic light emitting diodes (OLEDs), and solar panels. A large area substrate for manufacturing LCD, PDP, OLED or solar panels may be a glass or a polymer workpiece.
The large area substrate is typically subjected to a plurality of sequential processes to created devices, conductors, and insulators thereon. Each of these processes is generally performed in a process chamber configured to perform a single step of the production process. In order to efficiently complete the entire sequential processes, a number of process chambers are typically used. One fabrication process frequently used to process a large area substrate is plasma enhanced chemical vapor deposition (PECVD).
PECVD is generally employed to deposit thin films on a substrate such as a flat panel substrate or a semiconductor substrate. PECVD is typically performed in a vacuum chamber between parallel electrodes positioned several inches apart, typically with a variable gap for process optimization. A substrate being processed may be disposed on a temperature controlled substrate support disposed in the vacuum chamber. In some cases, the substrate support may be one of the electrodes. A precursor gas is introduced into the vacuum chamber and is typically directed through a distribution plate situated near the top of the vacuum chamber. The precursor gas in the vacuum chamber is then energized or excited into a plasma by applying a RF power coupled to the electrodes. The excited gas reacts to form a layer of material on a surface of the substrate positioned on the substrate support. Typically, a substrate support or a substrate support assembly in a PECVD chamber is configured to support and heat the substrate as well as serve as an electrode to excite the precursor gas.
Generally, large area substrates, for example those utilized for flat panel fabrication, are often exceeding 550 mm×650 mm, and are envisioned up to and beyond 4 square meters in surface area. Correspondingly, the substrate supports utilized to process large area substrates are proportionately large to accommodate the large surface area of the substrate. The substrate supports for high temperature use typically are casted, encapsulating one or more heating elements and thermocouples in an aluminum body. Due to the size of the substrate support, one or more reinforcing members are generally disposed within the substrate support to improve the substrate support's stiffness and performance at elevated operating temperatures (i.e., in excess of 350 degrees Celsius and approaching 500 degrees Celsius to minimize hydrogen content in some films). The aluminum substrate support is then anodized to provide a protective coating.
Although substrate supports configured in this manner have demonstrated good processing performance, two problems have been observed. The first problem is non-uniform deposition. Small local variations in film thickness, often manifesting as spots of thinner film thickness, have been observed which may be detrimental to the next generation of devices formed on large area substrates. It is believed that variation in substrate thickness and flatness, along with a smooth substrate support surface, typically about 50 micro-inches, creates a local capacitance variation in certain locations across the glass substrate, thereby creating local plasma non-uniformities that result on deposition variation, e.g., spots of thin deposited film thickness.
The second problem is caused by the static charge generated by the triboelectric process, or the process of bringing two materials into contact with each other and then separating them from each other. As a result, electrostatics may build up between the substrate and the substrate support making it difficult to separate the substrate from the substrate support once the process is completed.
An additional problem is known in the industry as the electro-static discharge (ESD) metal lines arcing problem. As the substrate size increased, the ESD metal lines become longer and larger. It is believed that the inductive current in the ESD metal lines becomes large enough during plasma deposition to damage the substrate. This ESD metal lines arcing problem has become a major recurring problem.
Therefore, there is a need for an improved substrate support.